The decision to proceed with a $110 million upgrade of Wellington Airport dovetails with the view of industry researcher Morningstar that Infratil is looking to Australia for growth opportunities.

Dual-listed Infratil last week gave the green light for the extension of the airport's terminal, as well as runway improvements and more parking, as part of an overall $250m plan.

Wellington Airport chief executive Steve Sanderson said the "short-term focus is very much about extending trans-Tasman opportunities, because that is where there is the opportunity to entice further operators to operate".

He said 84 airlines operated in Australia but Wellington Airport serviced flights only by Virgin, Qantas and Air NZ.

"Emirates operate trans-Tasman to Christchurch and Auckland particularly, and so does Air China.

"We're very keen on enticing those and equally Jetstar as well. [We are the] only major airport in New Zealand which Jetstar doesn't operate on across the Tasman, so we are continuously having discussions with them."

Statistics NZ figures show international passenger numbers nationally reached 10 million for the first time in the December 2013 year, with 5 million arrivals and 5 million departures.

Australia was still the dominant destination, accounting for about 1 million departures.

"Australia seems to be the market where Infratil, through its investments in Trustpower and Infratil Energy Australia, is looking for growth opportunities."

Infratil holds a 51 per cent stake in Trustpower, which is actively identifying and developing potential wind farm sites in South Australia, New South Wales and Victoria. It has two Australian wind farms generating electricity.

Morningstar maintained its fair value estimate of $2.50 per Infratil share on the NZX while rating the shares a "hold".

However, it raised its valuation for Infratil's Australian listed stock by 10c, to A$2.30 a share, to reflect the appreciation in the NZ dollar.

Morningstar lowered its forecast for Infratil following recent company guidance, with underlying earnings for 2014, before interest, tax, depreciation and amortisation (ebitda), estimated to drop by $58m to $490m.

It reflected a weaker trading performance at Trustpower, and NZ Bus, and the translation impact of a weaker Australian dollar.